954 research outputs found
Flow and acoustic characteristics of subsonic and supersonic jets from convergent nozzle
Acoustic and flow characteristics of subsonic and supersonic jets from convergent nozzle
MgB2 conductors for dc and ac applications
The paper presents discussion on up to date results on MgB2 conductors from
the point of view of their future dc and ac applications. Basic physical
parameters of MgB2 compound relevant to conductors are introduced. Different
conductor preparation methods and conductor architectures are presented and
attainable critical current densities discussed. Some numerical results on
critical currents and ac losses of future multifilamentary MgB2 conductors with
magnetic cladding of their filaments are given. Recently observed anomalous
decrease of ac susceptibility at 50 K in copper clad Powder-in-tube, PIT, MgB2
wires is presented.Comment: Paper presented at EUCAS'01 conference, Copenhagen, 26-30 August 200
Synthesis of as-grown superconducting MgB_2 thin films by molecular beam epitaxy in UHV conditions
As-grown superconducting MgB_2 thin films have been grown on SrTiO_3(001),
MgO(001), and Al_2O_3(0001) substrates by a molecular beam epitaxy (MBE) method
with novel co-evaporation conditions of low deposition rate in ultra-high
vacuum. The structural and physical properties of the films were studied by
RHEED, XRD, electrical resistivity measurements, and SQUID magnetometer. The
RHEED patterns indicate three-dimensional growth for MgB_2. The highest T_c
determined by resistivity measurement was about 36K in these samples. And a
clear Meissner effect below T_c was observed using magnetic susceptibility
measurement. We will discuss the influence of B buffer layer on the structural
and physical properties.Comment: 9 pages with 4 figures, ISS2003 proceedin
Superconducting magnesium diboride films with Tc \approx 24K grown by pulsed laser deposition with in-situ anneal
Thin superconducting films of magnesium diboride (MgB2) with Tc \approx 24K
were prepared on various oxide substrates by pulsed laser deposition (PLD)
followed by an in-situ anneal. A systematic study of the influence of various
in-situ annealing parameters shows an optimum temperature of about 600C in a
background of 0.7 atm. of Ar/4%H2 for layers consisting of a mixture of
magnesium and boron. Contrary to ex-situ approaches (e.g. reacting boron films
with magnesium vapor at 900C), these films are processed below the
decomposition temperature of MgB2. This may prove enabling in the formation of
multilayers, junctions, and epitaxial films in future work. Issues related to
the improvement of these films and to the possible in-situ growth of MgB2 at
elevated temperature are discussed.Comment: 5 pages, 4 figure
Electronic Structures of CaAlSi with Different Stacking AlSi Layers by First-Principles Calculations
The full-potential linear augmented plane-wave calculations have been applied
to investigate the systematic change of electronic structures in CaAlSi due to
different stacking sequences of AlSi layers. The present ab-initio calculations
have revealed that the multistacking, buckling and 60 degrees rotation of AlSi
layer affect the electronic band structure in this system. In particular, such
a structural perturbation gives rise to the disconnected and cylindrical Fermi
surface along the M-L lines of the hexagonal Brillouin zone. This means that
multistacked CaAlSi with the buckling AlSi layers increases degree of
two-dimensional electronic characters, and it gives us qualitative
understanding for the quite different upper critical field anisotropy between
specimens with and without superstructure as reported previously.Comment: 4 pages, 4 figures, to be published in J. Phys. Soc. Jp
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